Luca Smeraglia Talk

Polyphase Deformation and Lithological Controls on High-Grade Gold Ore Shoots at the Kokoseb Deposit

The Kokoseb gold deposit in the Damara Belt is hosted within metasedimentary rocks of the Kuiseb Formation, including quartz-biotite schists, biotite schists and meta-turbidites metamorphosed to mid- to upper amphibolite facies and affected by polyphase deformation. An early penetrative S1 schistosity, axial planar to inferred F1 isoclinal folds, is overprinted by N- to NE-plunging F2 folds developed around a central granodiorite dome. Gold mineralization forms a broad halo surrounding the intrusion and occurs as disseminated sulphides, quartz-sulphide veins, and quartz-feldspar-biotite-muscovite-sulphide veinlets transposed parallel to S1. The highest gold grades are associated with quartz-diopside-sulphide veins preferentially developed within competent meta-turbidites. Mineralization is strongly controlled by lithological competence contrasts and folding. Meta-turbidites provided high permeability and competence contrasts that enhanced hydrothermal fluid flow, veining and sulphide precipitation, whereas strongly schistose biotite schists are generally poorly mineralized. High-grade ore shoots are principally localized within F2-folded meta-turbidites and plunge parallel to F2 fold axes, particularly within the Central-Western Zone. These relationships indicate that gold deposition occurred during the late stages of deformation, probably synchronous with F2 folding and with the emplacement of the central granodiorite. These results offer new insights into the structural evolution of amphibolite-facies orogenic gold system in the Damara Belt.